Process for producing heterophasic copolymers of propylene

ABSTRACT

The present invention provides a process for producing a heterophasic copolymer composition. The polymerisation is conducted in the presence of an olefin polymerisation catalyst comprising a solid catalyst component further comprising titanium, magnesium, halogen and an internal donor, and a cocatalyst, the process comprising the steps of: (1) introducing streams of the solid catalyst component, the cocatalyst, propylene monomer and hydrogen into a first polymerisation reactor; (2) producing a first polymer of propylene in the first polymerisation reactor, the first polymer of propylene having a first melt flow rate MFR 2 of from 0.1 to 2.0 g/10 min; (3) withdrawing a stream comprising the first polymer of propylene from the first polymerisation reactor and passing it to a second polymerisation reactor; (4) introducing a stream of propylene monomer into the second polymerisation reactor; (5) producing a first polymer mixture comprising the first polymer of propylene and a second polymer of propylene in the second polymerisation reactor, the first polymer mixture having a second melt flow rate MFR 2  of from 0.05 to 1.0 g/10 min and which second melt flow rate is less than the first melt flow rate; (6) withdrawing a stream comprising the first polymer mixture from the second polymerisation reactor and passing it to a third polymerisation reactor; (7) introducing streams of propylene monomer and the comonomer into the third polymerisation reactor; (8) producing the heterophasic copolymer composition comprising the first polymer mixture and a third copolymer of propylene in the third polymerisation reactor, the heterophasic copolymer composition having a third melt flow rate MFR 2  of from 0.05 to 1.0 g/10 min, said heterophasic copolymer having a content of comonomer units of from 5 to 25% by mole; wherein the amount of xylene soluble fraction in the heterophasic copolymer determined according to ISO 16152 is from 14 to 35% by weight and intrinsic viscosity measured from the amorphous polymer (AM) of the heterophasic copolymer is from 1.5 to 4.4 dl/g; and (9) recovering the heterophasic copolymer composition from the third polymerisation reactor; characterised in that the internal donor is a compound having the structure according to formula (I); wherein R 1  and R2 are the same or different being a linear or branched C 1 -C 12 -alkyl group and R is hydrogen or a linear, branched or cyclic C 1  to C 12 -alkyl.

FIELD OF THE INVENTION

The present invention is directed to a process for producing propylenepolymers. In specific, the present invention is directed to a processfor producing impact-resistant copolymers of propylene. The presentinvention is also directed to a process for producing heterophasiccopolymers of propylene comprising a semicrystalline matrix and anamorphous copolymer phase dispersed within the matrix. The presentinvention is further directed to a process suitable for making pipeshaving good low-temperature toughness.

PROBLEM TO BE SOLVED

EP-A-2796472 discloses a process where propylene is polymerised in twostages so that a low molecular weight propylene homopolymer is producedin the first stage and a high molecular weight propylene copolymer isproduced in the second stage.

EP-A-2796473 discloses a process where propylene was polymerised inthree stages. In the first stage a low molecular weight homopolymer ofpropylene was produced, in the second stage a high molecular weightcopolymer was produced and in the third stage a copolymer of propylenewas produced containing from 10 to 40% by mole, preferably from 15 to30% by mole of comonomer units.

EP-A-2610271 discloses a solid catalyst component for propylenepolymerisation. The catalyst contains an internal donor which is acompound selected from benzoates, alkylene glycol dibenzoates, maleates,1-cyclohexene-1,2-dicarboxylic dialkylesters and 1,3-diethers, or amixture of any of such compounds.

SUMMARY OF THE INVENTION

As seen from one aspect, the present invention provides a process forproducing a heterophasic copolymer composition comprising propylenemonomer and a comonomer selected from ethylene, alpha-olefins having 4to 10 carbon atoms and their mixtures, in the presence of an olefinpolymerisation catalyst comprising a solid catalyst component furthercomprising titanium, magnesium, halogen and an internal donor, and acocatalyst, the process comprising the steps of: (1) introducing streamsof the solid catalyst component, the cocatalyst, propylene monomer andhydrogen into a first polymerisation reactor; (2) producing a firstpolymer of propylene in the first polymerisation reactor, the firstpolymer of propylene having a first melt flow rate MFR₂ of from 0.1 to2.0 g/10 min; (3) withdrawing a stream comprising the first polymer ofpropylene from the first polymerisation reactor and passing it to asecond polymerisation reactor; (4) introducing a stream of propylenemonomer into the second polymerisation reactor; (5) producing a firstpolymer mixture comprising the first polymer of propylene and a secondpolymer of propylene in the second polymerisation reactor, the firstpolymer mixture having a second melt flow rate MFR₂ of from 0.05 to 1.0g/10 min and which second melt flow rate is less than the first meltflow rate; (6) withdrawing a stream comprising the first polymer mixturefrom the second polymerisation reactor and passing it to a thirdpolymerisation reactor; (7) introducing streams of propylene monomer andthe comonomer into the third polymerisation reactor; (8) producing theheterophasic copolymer composition comprising the first polymer mixtureand a third copolymer of propylene in the third polymerisation reactor,the heterophasic copolymer composition having a third melt flow rateMFR₂ of from 0.05 to 1.0 g/10 min, said heterophasic copolymer having acontent of comonomer units of from 5 to 25% by mole; wherein the amountof xylene soluble fraction in the heterophasic copolymer determinedaccording to ISO 16152 is from 14 to 35% by weight and intrinsicviscosity measured from the amorphous polymer (AM) of the heterophasiccopolymer is from 1.5 to 4.4 dl/g; and (9) recovering the heterophasiccopolymer composition from the third polymerisation reactor;characterised in that the internal donor is a compound having thestructure according to formula (I):

wherein R₁ and R₂ are the same or different being a linear or branchedC₁-C₁₂-alkyl group and R is hydrogen or a linear, branched or cyclic C₁to C₁₂-alkyl.

As seen from another aspect, the present invention provides aheterophasic copolymer obtainable by the process as defined above theheterophasic copolymer comprising (A) a first polymer of propylene,selected from homopolymers of propylene and random copolymers ofpropylene containing from 0.1 to 5% by mole of a comonomer selected fromthe group consisting of ethylene, alpha-olefins having from 4 to 10carbon atoms, and mixtures thereof and having a melt flow rate MFR₂ offrom 0.1 to 4.0 g/10 min; (B) a second polymer of propylene, selectedfrom homopolymers of propylene and random copolymers of propylenecontaining from 0.1 to 5% by mole of a comonomer selected from the groupconsisting of ethylene, alpha-olefins having from 4 to 10 carbon atoms,and mixtures thereof and having a melt flow rate MFR₂ of from 0.05 to0.3 g/10 min and which is less than the MFR₂ of the first polymer ofpropylene; (C) a third polymer of propylene selected from randomcopolymers of propylene containing from 35 to 75% by mole of units of acomonomer selected from the group consisting of ethylene, alpha-olefinshaving from 4 to 10 carbon atoms and mixtures thereof; and wherein theheterophasic copolymer contains from 1 to 30 ppm magnesium originatingfrom the catalyst and no phthalic acid esters originating from thecatalyst.

As seen from a further aspect, the present invention provides pipeshaving good low-temperature toughness made of the heterophasic copolymerof propylene as defined above.

DETAILED DESCRIPTION

According to the present invention propylene is polymerised in threereactors. A heterophasic copolymer of propylene with a comonomerselected from ethylene, alpha-olefins having 4 to 10 carbon atoms andtheir mixtures is produced in the process. Further on, said heterophasiccopolymer may be processed into a pipe having good low-temperaturetoughness.

A heterophasic copolymer comprises at least two phases, a matrix and anelastomeric phase.

The matrix, which is the continuous phase, substantially comprises andpreferably consists of a semicrystalline homopolymer of propylene or arandom copolymer of propylene with a comonomer selected from ethylene,alpha-olefins having 4 to 10 carbon atoms and their mixtures. By“semicrystalline” is meant that the homopolymer or the random copolymerhas a substantial crystallinity. This is indicated, for instance, by thefact that matrix is mostly insoluble in cold xylene determined accordingto ISO 16152. By “mostly insoluble” is meant that at most 30%,preferably at most 15% and more preferably at most 10% by weight of thematrix is soluble in xylene at 25° C. according to ISO 16152.

By “substantially comprises” is here meant that substantially all, thatis, at least 90% by weight, preferably at least 95% by weight and morepreferably at least 98% and especially preferably at least 99% by weightof the matrix is formed of the homopolymer of propylene or the randomcopolymer of propylene with a comonomer selected from ethylene,alpha-olefins having 4 to 10 carbon atoms and their mixtures. It is,however, within the scope of the invention that the matrix consists oftwo or more homopolymers of propylene and/or random copolymers ofpropylene as defined above, provided that the overall matrix issemicrystalline and forms a single, continuous phase.

The matrix comprises a higher molecular weight component produced in onepolymerisation reactor and a lower molecular weight component producedin another polymerisation reactor.

The elastomeric phase is dispersed into the matrix. The elastomericphase substantially comprises, preferably consists of, copolymers ofpropylene with a comonomer selected from ethylene, alpha-olefins having4 to 10 carbon atoms and their mixtures. The elastomeric phase issubstantially amorphous with no crystalline fraction. This is indicated,for instance, by the fact that elastomeric phase is mostly soluble incold xylene as measured according to ISO 16152. Thus, at least about80%, preferably at least 85%, more preferably at least 90% andespecially preferably at least 95% of the elastomeric phase is solublein cold xylene as measured according to ISO 16152.

It is within the scope of the invention that the elastomeric phaseconsists of two or more copolymers of propylene as defined above,provided that the overall elastomeric phase is non-crystalline and isdispersed within the matrix as separate domains.

Further the heterophasic polypropylene may contain to some extent acrystalline polyethylene, which is a by-reaction product obtained by thepreparation of the heterophasic propylene copolymer. Such crystallinepolyethylene is present as inclusion of the amorphous phase due tothermodynamic reasons.

Especially, according to the present invention the matrix is produced inat least two distinct polymerisation steps in at least twopolymerisation reactors and the elastomeric phase is produced in atleast one polymerisation step in at least one polymerisation reactor. Toavoid unnecessary complexity of the process it is preferred that thematrix is produced in two polymerisation reactors and the elastomericphase in one or two polymerisation reactors.

Catalyst

Solid Catalyst Component

The solid catalyst component used in the present invention is preferablya solid Ziegler-Natta catalyst component, which comprises compounds of atransition metal of Group 4 to 6 of IUPAC, like titanium, a Group 2metal compound, like a magnesium and an internal electron donor (ID)being a compound according to formula (I). Thus, the catalyst is fullyfree of undesired phthalic compounds. Further, the solid catalystcomponent is free of any external support material, like silica orMgCl₂, but the catalyst is self-supported.

In the formula (I) above R₁ and R₂ are the same or different being alinear or branched C₁-C₁₂-alkyl group and R is hydrogen or a linear,branched or cyclic C₁ to C₁₂-alkyl.

The solid catalyst component in particulate form is preferably producedby the following general procedure:

-   -   a) providing a solution of    -   a₁) at least a Group 2 metal alkoxy compound (Ax) being the        reaction product of a Group 2 metal compound and an alcohol (A)        comprising in addition to the hydroxyl moiety at least one ether        moiety optionally in an organic liquid reaction medium; or    -   a₂) at least a Group 2 metal alkoxy compound (Ax′) being the        reaction product of a Group 2 metal compound and an alcohol        mixture of the alcohol (A) and a monohydric alcohol (B) of        formula R³OH, optionally in an organic liquid reaction medium;        or    -   a₃) a mixture of the Group 2 metal alkoxy compound (Ax) and a        Group 2 metal alkoxy compound (Bx) being the reaction product of        a Group 2 metal compound and the monohydric alcohol (B),        optionally in an organic liquid reaction medium; or    -   a₄) Group 2 metal alkoxy compound of formula        M(OR⁴)_(n)(OR⁵)_(m)X_(2-n-m) or mixture of Group 2 alkoxides        M(OR⁴)_(n)X_(2-n′) and M(OR⁵)_(m′)X_(2-m′), where M is Group 2        metal, X is halogen, R⁴ and R⁵ are different alkyl groups of C₂        to C₁₆ carbon atoms, and 0≤n<2, 0≤m<2 and n+m+(2−n−m)=2,        provided that both n and m are not simultaneously zero, 0 <n′≤2        and 0<m′≤2; and    -   b) adding said solution from step a) to at least one compound of        a transition metal of Group 4 to 6 and    -   c) obtaining the solid catalyst component particles, and adding        the internal electron donor compound according to the        formula (I) at any step prior to step c).

The internal donor (ID) or precursor thereof is thus added preferably tothe solution of step a) or to the transition metal compound beforeadding the solution of step a).

According to the procedure above the solid catalyst component can beobtained via precipitation method or via emulsion—solidification methoddepending on the physical conditions, especially temperature used insteps b) and c). Emulsion is also called liquid/liquid two-phase system.

In both methods (precipitation or emulsion-solidification) the catalystchemistry is the same.

In precipitation method combination of the solution of step a) with atleast one transition metal compound in step b) is carried out and thewhole reaction mixture is kept at least at 50° C., more preferably inthe temperature range of 55 to 110° C., more preferably in the range of70 to 100° C., to secure full precipitation of the catalyst component inform of a solid particles (step c).

In emulsion—solidification method in step b) the solution of step a) istypically added to the at least one transition metal compound at a lowertemperature, such as from −10 to below 50° C., preferably from −5 to 30°C. During agitation of the emulsion the temperature is typically kept at−10 to below 40° C., preferably from −5 to 30° C. Droplets of thedispersed phase of the emulsion form the active catalyst composition.Solidification (step c) of the droplets is suitably carried out byheating the emulsion to a temperature of 70 to 150° C., preferably to 80to 110° C.

The catalyst preparation process according to emulsion—solidificationmethod is preferably used in the present invention.

Preferably the Group 2 metal is magnesium. The magnesium alkoxycompounds (Ax), (Ax′) and (Bx) can be prepared in situ in the first stepof the catalyst preparation process, step a), by reacting the magnesiumcompound with the alcohol(s) as described above, or said magnesiumalkoxy compounds can be separately prepared magnesium alkoxy compoundsor they can be even commercially available as ready magnesium alkoxycompounds (a₄)) and used as such in the catalyst preparation process ofthe invention.

In a preferred embodiment in step a) the solution of a₂) or a₃) areused, i.e. a solution of (Ax′) or a solution of a mixture of (Ax) and(Bx).

Illustrative examples of alcohols (A) are glycol monoethers. Preferredalcohols (A) are C₂ to C₄ glycol monoethers, wherein the ether moietiescomprise from 2 to 18 carbon atoms, preferably from 4 to 12 carbonatoms. Preferred examples are 2-(2-ethylhexyloxy)ethanol, 2-butyloxyethanol, 2-hexyloxy ethanol and 1,3-propylene-glycol-monobutyl ether,3-butoxy-2-propanol, with 2-(2-ethylhexyloxy)ethanol and1,3-propylene-glycol-monobutyl ether, 3-butoxy-2-propanol beingparticularly preferred.

Illustrative monohydric alcohols (B) are of formula R³OH, with R³ beingstraight-chain or branched C₂-C₁₆ alkyl residue, preferably C₄ to C₁₀,more preferably C₆ to C₈ alkyl residue The most preferred monohydricalcohol is 2-ethyl-1-hexanol or octanol.

Preferably a mixture of Mg alkoxy compounds (Ax) and (Bx) or mixture ofalcohols (A) and (B), respectively, are used and employed in a moleratio of Bx:Ax or B:A from 10:1 to 1:10, more preferably 6:1 to 1:6,still more preferably 5:1 to 1: 3, most preferably 5:1 to 3:1.

Magnesium alkoxy compound may be a reaction product of alcohol(s), asdefined above, and a magnesium compound selected from dialkylmagnesiums, alkyl magnesium alkoxides, magnesium dialkoxides, alkoxymagnesium halides and alkyl magnesium halides. Further, magnesiumdialkoxides, magnesium diaryloxides, magnesium aryloxyhalides, magnesiumaryloxides and magnesium alkyl aryloxides can be used. Alkyl groups canbe similar or different C₁-C₂₀ alkyls, preferably C₂-C₁₀ alkyl. Typicalalkyl-alkoxy magnesium compounds, when used, are ethyl magnesiumbutoxide, butyl magnesium pentoxide, octyl magnesium butoxide and octylmagnesium octoxide. Preferably the dialkyl magnesiums are used. Mostpreferred dialkyl magnesiums are butyl octyl magnesium or butyl ethylmagnesium.

It is also possible that magnesium compound can react in addition to thealcohol (A) and alcohol (B) also with a polyhydric alcohol (C) offormula R″ (OH)_(m) to obtain said magnesium alkoxide compounds.Preferred polyhydric alcohols, if used, are alcohols, wherein R″ is astraight-chain, cyclic or branched C₂ to C₁₀ hydrocarbon residue, and mis an integer of 2 to 6.

The magnesium alkoxy compounds of step a) are thus selected from thegroup consisting of magnesium dialkoxides, diaryloxy magnesiums,alkyloxy magnesium halides, aryloxy magnesium halides, alkyl magnesiumalkoxides, aryl magnesium alkoxides and alkyl magnesium aryloxides. Inaddition a mixture of magnesium dihalide and a magnesium dialkoxide canbe used.

The solvents to be employed for the preparation of the present solidcatalyst component may be selected among aromatic and aliphatic straightchain, branched and cyclic hydrocarbons with 5 to 20 carbon atoms, morepreferably 5 to 12 carbon atoms, or mixtures thereof. Suitable solventsinclude benzene, toluene, cumene, xylol, pentane, hexane, heptane,octane and nonane. Hexanes and pentanes are particularly preferred.

The reaction for the preparation of the magnesium alkoxy compound may becarried out at a temperature of 40° to 70° C. Most suitable temperatureis selected depending on the Mg compound and alcohol(s) used.

The transition metal compound of Group 4 to 6 is preferably a titaniumcompound, most preferably a titanium halide, like TiCl₄.

The internal donor (ID) used in the preparation of the catalyst used inthe present invention is a compound according to formula (I).

Preferably R is hydrogen or methyl. Most preferred examples are e.g.substituted maleates and citraconates, especially preferablycitraconates.

In emulsion method, the two phase liquid-liquid system may be formed bysimple stirring and optionally adding (further) solvent(s) andadditives, such as the turbulence minimizing agent (TMA) and/or theemulsifying agents and/or emulsion stabilizers, like surfactants, whichare used in a manner known in the art for facilitating the formation ofand/or stabilize the emulsion. Preferably, surfactants are acrylic ormethacrylic polymers. Particular preferred are unbranched C₁₂ to C₂₀(meth)acrylates such as poly(hexadecyl)-methacrylate andpoly(octadecyl)-methacrylate and mixtures thereof. Turbulence minimizingagent (TMA), if used, is preferably selected from a-olefin polymers ofone or more a-olefin monomers with 2 to 20 carbon atoms, preferably from6 to 20 carbon atoms. Suitable examples of monomers are 1-octene,1-nonene, 1-decene, 1-undecene and 1-dodecene and mixtures thereof. Mostpreferably at least one of the monomers is 1-decene.

The solid particulate product obtained by precipitation oremulsion—solidification method may be washed at least once, preferablyat least twice, most preferably at least three times with an aromaticand/or aliphatic hydrocarbons, preferably with toluene, heptane orpentane and/or with TiCl₄ Washing solutions can also contain donorsand/or compounds of Group 13, like trialkyl aluminium, halogenated alkylaluminium compounds or alkoxy aluminium compounds. Aluminium compoundscan also be added during the catalyst synthesis.

The catalyst can further be dried, as by evaporation or flushing withnitrogen or it can be slurried to an oily liquid without any dryingstep.

The finally obtained Ziegler-Natta catalyst is desirably in the form ofparticles having generally an average particle size range of 5 to 200μm, preferably 10 to 100 μm. Particles are compact with low porosity andhave surface area below 20 g/m², more preferably below 10 g/m².

Typically the amount of Ti is 1-6 wt-%, Mg 10 to 20 wt-% and donor 10 to40 wt-% of the catalyst composition.

Detailed description of preparation of solid catalyst components isdisclosed in WO-A-2012/007430, EP-A-2610271, EP-A-261027 andEP-A-2610272.

Cocatalyst

The solid catalyst component is combined with a cocatalyst before it isused in the polymerisation. The cocatalyst typically comprises analuminium alkyl compound and an external electron donor.

The external donor (ED) is preferably present. Suitable external donors(ED) include certain silanes, ethers, esters, amines, ketones,heterocyclic compounds and blends of these. The external donor (ED) isespecially preferably a silane.

It is most preferred to use silanes of the general formula

R^(a) _(p)R^(b) _(q)Si(OR^(c))_((4-p-q))   (II)

wherein R^(a), R^(b) and R^(c) can be chosen independently from oneanother and can be the same or different and denote a hydrocarbonradical, in particular an alkyl or cycloalkyl group, and wherein p and qare numbers ranging from 0 to 3 with their sum p+q being equal to orless than 3. Examples of such commonly used silanes are(tert-butyl)₂Si(OCH₃)₂, (cyclohexyl)(methyl)Si(OCH₃)²,(phenyl)₂Si(OCH₃)₂ and (cyclopentyl)₂Si(OCH₃)₂.

Another preferred group of silanes have the general formula

Si(OCH₂CH₃)₃(NR^(d)R^(e))   (III)

wherein R³ and R⁴ can be the same or different a represent a linear,branched or cyclic hydrocarbon group having 1 to 12 carbon atoms.

It is in particular preferred that R^(d) and R^(e) are independentlyselected from the group consisting of methyl, ethyl, n-propyl, n-butyl,octyl, decanyl, iso-propyl, iso-butyl, iso-pentyl, tert.-butyl,tert.-amyl, neopentyl, cyclopentyl, cyclohexyl, methylcyclopentyl andcycloheptyl, and most preferably R^(d) and R^(e) are ethyl.

In addition to the optional external donor (ED) the co-catalystcomprises an aluminium alkyl compound. The aluminium alkyl compound ispreferably an aluminum alkyl or aluminum alkyl halide compound.Accordingly in one specific embodiment the aluminium alkyl compound is atrialkylaluminium, like triethylaluminium (TEAL), trimethylaluminium,tri-isobutylaluminium, trioctylaluminium or tri-n-hexylaluminium. Inanother embodiment the aluminium alkyl compound is a dialkyl aluminiumchloride or alkyl aluminium dichloride or mixtures thereof, such asdiethylaluminium chloride, dimethylaluminium chloride, ethylaluminiumdichloride or ethylaluminium sesquichlorde. Especially preferably thealuminium alkyl compound is triethylaluminium (TEAL).

The ratio of the aluminium alkyl compound (Al) to the external donor(ED) [Al/ED] and/or the ratio of aluminium alkyl compound (Al) to thetransition metal (TM) [Al/TM] should be chosen for each combination ofaluminium alkyl compound and external donor. The required ratios arewell known to the person skilled in the art.

First Polymerisation Reactor

In the first polymerisation reactor the first polymer of propylene,which is the lower molecular weight component of the matrix, is producedin the presence of the polymerisation catalyst, propylene and hydrogen.Optionally, a comonomer may also be present.

In the first polymerisation reactor the polymerisation is preferablyconducted as slurry polymerisation. In such a case the reactor may beany reactor suitable for slurry polymerisation, such as a stirred tankreactor or a loop reactor. Preferably the first polymerisation reactoris a loop reactor.

In the first polymerisation reactor the polymerisation is conducted at atemperature which is less than the melting temperature of thepolypropylene. The temperature is typically selected to be within therange of from 50 to 100° C., preferably from 55 to 95° C. and morepreferably from 60 to 90° C. The pressure is typically from 1 to 150bar, preferably from 10 to 100 bar. Generally the temperature and thepressure are selected so that the fluid within the reactor forms asingle phase, such as a liquid phase or a supercritical phase.

In slurry polymerisation the polymer particles, in which the catalyst isfragmented and dispersed, are suspended in a fluid diluent, typically aliquid diluent. The diluent is typically formed of propylene monomer,which the other reactants, such as hydrogen and comonomer, are dissolvedin. The diluent may contain minor amount of inert components, such aspropane, which are present as impurities in the reactants.

The first polymer of propylene may be a homopolymer of propylene or acopolymer of propylene with a comonomer selected from ethylene,alpha-olefins having 4 to 10 carbon atoms and their mixtures. If thefirst polymer of propylene is a copolymer then is the first polymercontains from 0.1 to 6% by mole of units derived from the comonomer andfrom 94 to 99.9% by mole of propylene units. Preferably, the firstpolymer then contains from 0.1 to 2% by mole of units derived from thecomonomer and from 98 to 99.9% by mole of propylene units. However,preferably the first polymer of propylene is a homopolymer of propyleneand does not contain comonomer units.

The first polymer of propylene has a melt index MFR₂ of from 0.1 to 4.0g/10 min. Preferably the melt index MFR₂ of the first polymer ofpropylene is from 0.2 to 3.0 g/10 min and more preferably from 0.2 to2.0 g/10 min. It is important that the melt index of the first copolymerremains within these limits. If the melt index is greater, then agreater amount of hydrogen would be needed to reach the melt index and aseparation step to remove hydrogen would be needed. Otherwise it wouldnot be possible to reach the desired melt index in the secondpolymerisation stage. On the other hand, a too low melt index of thefirst polymer of propylene would lead to an insufficiently narrowmolecular weight distribution and thus unacceptable polymer properties.

The first polymer of propylene is semicrystalline and not amorphous.Therefore it has a substantial fraction which is not soluble in xyleneat 25° C. The first polymer of propylene preferably has a content ofxylene soluble fraction of from 0.1 to 10% by weight, preferably from0.5 to 5% by weight.

The polymerisation in the first polymerisation reactor is preferablyconducted in slurry in a loop reactor. Then the polymer particles formedin the polymerisation, together with the catalyst fragmented anddispersed within the particles, are suspended in the fluid hydrocarbon.The slurry is agitated to enable the transfer of reactants from thefluid into the particles. In loop reactors the slurry is circulated witha high velocity along a closed pipe by using a circulation pump. Loopreactors are well known in the art and examples are given, for instance,in U.S. Pat. No. 4,582,816, U.S. Pat. No. 3,405,109, U.S. Pat. No.3,324,093, EP-A-479186 and U.S. Pat. No. 5,391,654.

The slurry may be withdrawn from the reactor either continuously orintermittently. A preferred way of intermittent withdrawal is the use ofsettling legs where the solids concentration of the slurry is allowed toincrease before withdrawing a batch of the concentrated slurry from thereactor. It is, however, preferred to withdraw slurry continuously fromthe reactor. Continuous withdrawal is disclosed, among others, inEP-A-891990, EP-A-1415999, EP-A-1591460 and EP-A-1860125. The continuouswithdrawal may be combined with a suitable concentration method, asdisclosed in EP-A-1860125 and EP-A-1591460.

Into the slurry polymerisation stage other components are alsointroduced as it is known in the art. Thus, hydrogen is used to controlthe molecular weight of the polymer. Process additives, such asantistatic agent, may be introduced into the reactor to facilitate astable operation of the process.

Hydrogen feed is typically adjusted to maintain constant hydrogen topropylene ratio within the loop reactor. The ratio is maintained at sucha value that the melt index MFR₂ of the first copolymer is at thedesired value. While the actual value of the required hydrogen topropylene ratio depends, among others, on the catalyst andpolymerisation conditions it has been found that when the ratio iswithin the range of from 0.05 to 1.0 mol/kmol (or, mol/1000 mol),preferably from 0.05 to 0.5 mol/kmol, good results have been obtained.

Comonomer feed, if comonomer is used, is typically adjusted to maintainconstant comonomer to propylene ratio within the loop reactor. The ratiois maintained at such a value that the comonomer content of the firstcopolymer is at the desired value. While the actual value of therequired comonomer to propylene ratio depends, among others, on thecatalyst, type of comonomer and polymerisation conditions it has beenfound that when the ratio is within the range of from 0.1 to 2 mol/kmol,preferably from 0.1 to 1 mol/kmol good results have been obtained.However, preferably comonomer is not introduced into the firstpolymerisation reactor.

According to the present invention the slurry is passed directly fromthe first polymerisation reactor into the second polymerisation reactor.By “directly” it is meant that the slurry is introduced from the firstreactor into the second reactor without a flash step between thereactors for removing at least a part of the reaction mixture from thepolymer. Thereby, substantially the entire slurry stream withdrawn fromthe first polymerisation reactor is passed to the second polymerisationreactor. This kind of direct feed is described in EP-A-887379,EP-A-887380, EP-A-887381 and EP-A-991684. However, it is within thescope of the present invention to take small samples or sample streamsfrom the polymer or from the fluid phase or from both for analysing thepolymer and/or the composition of the reaction mixture. As understood bythe person skilled in the art, the volume of such sample streams issmall compared to the total slurry stream withdrawn from the loopreactor and typically much less than 1% by weight of the total stream,such as at most 0.1% or 0.01% or even 0.001% by weight.

Second Polymerisation Reactor

In the second polymerisation reactor a first polymer mixture comprisingthe first polymer of propylene and a second polymer of propylene isformed. This is done by introducing the particles of the first polymer,containing active catalyst dispersed therein, together with additionalpropylene and optionally hydrogen and comonomer into the secondpolymerisation reactor. This causes the second polymer of propylene toform on the particles containing the first polymer of propylene.

The second polymerisation is preferably conducted in a fluidised bed gasphase reactor. Typically the second polymerisation reactor is thenoperated at a temperature within the range of from 50 to 100° C.,preferably from 65 to 90° C. The pressure is suitably from 10 to 40 bar,preferably from 15 to 30 bar.

The comonomer, if used, is selected from ethylene, alpha-olefinscontaining 4 to 10 carbon atoms and their mixtures. The comonomer usedin the second polymerisation reactor may be the same as or differentfrom the comonomer used in the first polymerisation reactor. Preferablythe same comonomer is used in the first and the second polymerisationreactors, if any is used. Especially preferably the comonomer is thenethylene.

Also in the second polymerisation reactor the content of the eventualcomonomers is controlled to obtain the desired comonomer content of thefirst copolymer mixture. If a comonomer is present then typically thefirst polymer mixture contains from 0.1 to 2% by mole of units derivedfrom the comonomer and from 98 to 99.9% by mole of propylene units.Preferably the copolymer mixture contains from 0.2 to 1% by mole ofunits derived from the comonomer and from 99 to 99.8% by mole ofpropylene units. Furthermore, the comonomer content of the copolymermixture is preferably greater than the comonomer content of the firstpolymer of propylene. Preferably the ratio of the comonomer content ofthe first copolymer to the comonomer content of the copolymer mixture(both expressed in mol-%), C₁/C_(b), is not greater than 0.95, morepreferably not greater than 0.9 and especially preferably not greaterthan 0.8.

Preferably no comonomer is present in the second polymerisation reactor.Thereby the second polymer of propylene is a second homopolymer ofpropylene. It was also preferred that the first polymer of propylene wasthe first homopolymer of propylene and thereby the first polymer mixtureis preferably the first homopolymer mixture.

The second polymer of propylene produced in the second polymerisationreactor is semicrystalline and not amorphous. Therefore it has asubstantial fraction which is not soluble in xylene at 25° C. The firstpolymer mixture preferably has a content of xylene soluble fraction offrom 0.1 to 10% by weight, more preferably from 0.5 to 5% by weight.

The melt index MFR₂ of the first polymer mixture is from 0.05 to 2.0g/10 min. Preferably the melt index MFR₂ of the first polymer mixture isfrom 0.07 to 1.0 g/10 min, more preferably from 0.1 to 0.5 g/10 min.Furthermore, the melt index of the first polymer mixture is less thanthe melt index of the first polymer of propylene. Preferably, the ratioof the melt index of the first polymer mixture to the melt index of thefirst polymer of propylene, MFR_(2,b)/MFR_(2,1), has a value of notgreater than 0.8, more preferably not greater than 0.7 and in particularnot greater than 0.6. Furthermore, preferably the ratio of the meltindex of the first polymer mixture to the melt index of the firstpolymer of propylene, MFR_(2,b)/MFR_(2,1), has a value of at least 0.2,more preferably at least 0.3 and in particular at least 0.35.

As it is well known in the art the melt index MFR₂ of the second polymerof propylene produced in the second polymerisation reactor cannot bedirectly measured because the second polymer of propylene cannot beisolated from the first polymer mixture. However, by knowing the weightfractions of the first and second polymers in the polymer mixture andthe melt indices of the first polymer and the polymer mixture it ispossible to calculate the MFR₂ of the second polymer. This can be doneby using the equation

$\begin{matrix}{{MI}_{b} = ( {{w_{1} \cdot {MI}_{1}^{- 0.0965}} + {w_{2} \cdot {MI}_{2}^{- 0.0965}}} )^{- \frac{1}{0.0965}}} & ( {{eq}.\mspace{14mu} 1} )\end{matrix}$

Where w is the weight fraction of the component in the mixture, MI isthe melt index MFR₂ and subscripts b, 1 and 2 refer to the mixture,component 1 and component 2, respectively. By calculating the MFR₂ ofthe second polymer of propylene it can be found to lie within the rangeof from 0.05 to 0.3 g/10 min, preferably 0.1 to 0.3 g/10 min.

Also the comonomer content of the second polymer cannot be directlymeasured. However, by using the standard mixing rule it can becalculated from the comonomer contents of the copolymer mixture and thefirst polymer.

C _(b) =w ₁ ·C ₁ +w ₂ ·C ₂   (eq. 2)

where C is the content of comonomer in weight-%, w is the weightfraction of the component in the mixture and subscripts b, 1 and 2 referto the overall mixture, component 1 and component 2, respectively.

As it is well known to the person skilled in the art the comonomercontent in weight basis in a binary copolymer can be converted to thecomonomer content in mole basis by using the following equation

$\begin{matrix}{c_{m} = \frac{1}{1 + {( {\frac{1}{c_{w}} - 1} ) \cdot \frac{{MW}_{c}}{{MW}_{m}}}}} & ( {{eq}.\mspace{14mu} 3} )\end{matrix}$

where c_(m) is the mole fraction of comonomer units in the copolymer,c_(w) is the weight fraction of comonomer units in the copolymer, MW_(c)is the molecular weight of the comonomer (such as ethylene) and MW_(m)is the molecular weight of the main monomer (i.e., propylene).

The content of the xylene soluble polymer in the second copolymer cannotbe directly measured. The content can be estimated, however, by usingthe standard mixing rule:

XS_(b) =w ₁ ·XS ₁ +w ₂ ·XS ₂   (eq.4)

where XS is the content of xylene soluble polymer in weight-%, w is theweight fraction of the component in the mixture and subscripts b, 1 and2 refer to the overall mixture, component 1 and component 2,respectively. The second copolymer typically can be found to have acontent of xylene soluble polymer of not greater than 10% by weight,preferably not greater than 5% by weight.

The first polymer mixture preferably comprises from 35 to 60% by weightof the first polymer of propylene and from 40 to 65% by weight of thesecond polymer of propylene.

When the entire slurry stream from the first polymerisation reactor isintroduced into the second polymerisation reactor then substantialamounts of propylene, eventual comonomer and hydrogen are introducedinto the second polymerisation reactor together with the polymer.However, this is generally not sufficient to maintain desired propyleneconcentration in the second polymerisation reactor. Therefore additionalpropylene is typically introduced into the second polymerisationreactor. It is introduced to maintain a desired propylene concentrationin the fluidisation gas.

It is also often necessary to introduce additional hydrogen into thesecond polymerisation reactor to control the melt index of the firstpolymer mixture. Suitably, the hydrogen feed is controlled to maintainconstant hydrogen to propylene ratio in the fluidisation gas. The actualratio depends on the catalyst. Good results have been obtained bymaintaining the ratio within the range of from 0.1 to 3 mol/kmol,preferably from 0.15 to 2 mol/kmol.

In a fluidised bed gas phase reactor olefins are polymerised in thepresence of a polymerisation catalyst in an upwards moving gas stream.The reactor typically contains a fluidised bed comprising the growingpolymer particles containing the active catalyst, said fluidised bedhaving its base above a fluidisation grid.

The polymer bed is fluidized with the help of the fluidisation gascomprising the olefin monomer, eventual comonomer(s), eventual chaingrowth controllers or chain transfer agents, such as hydrogen, andeventual inert gas. The fluidisation gas is introduced into an inletchamber at the bottom of the reactor. To make sure that the gas flow isuniformly distributed over the cross-sectional surface area of the inletchamber the inlet pipe may be equipped with a flow dividing element asknown in the art, e.g. U.S. Pat. No. 4,933,149 and EP-A-684871. One ormore of the above-mentioned components may be continuously added intothe fluidisation gas for compensating losses caused, among other, byreaction or product withdrawal.

From the inlet chamber the gas flow is passed upwards through afluidisation grid into the fluidised bed. The purpose of thefluidisation grid is to divide the gas flow evenly through thecross-sectional area of the bed. Sometimes the fluidisation grid may bearranged to establish a gas stream to sweep along the reactor walls, asdisclosed in WO-A-2005/087361. Other types of fluidisation grids aredisclosed, among others, in U.S. Pat. No. 4,578,879, EP-A600414 andEP-A-721798. An overview is given in Geldart and Bayens: The Design ofDistributors for Gas-fluidized Beds, Powder Technology, Vol. 42, 1985.

The fluidisation gas passes through the fluidised bed. The superficialvelocity of the fluidisation gas must be greater than minimumfluidisation velocity of the particles contained in the fluidised bed,as otherwise no fluidisation would occur. On the other hand, thevelocity of the gas should be less than the transport velocity, asotherwise the whole bed would be entrained with the fluidisation gas.The bed voidage then is then typically less than 0.8, preferably lessthan 0.75 and more preferably less than 0.7. Generally the bed voidageis at least 0.6. An overview is given, among others in Geldart: GasFluidization Technology, J.Wiley & Sons, 1986 in chapters 2.4 and 2.5(pages 17-18) as well as in chapters 7.3 to 7.5 (pages 169-186,especially FIG. 7.21 on page 183).

When the fluidisation gas is contacted with the bed containing theactive catalyst the reactive components of the gas, such as monomers andchain transfer agents, react in the presence of the catalyst to producethe polymer product. At the same time the gas is heated by the reactionheat.

The unreacted fluidisation gas is removed from the top of the reactorand cooled in a heat exchanger to remove the heat of reaction. The gasis cooled to a temperature which is less than that of the bed to preventthe bed from heating because of the reaction. It is possible to cool thegas to a temperature where a part of it condenses. When the liquiddroplets re-enter the fluidised bed they are vaporised. The vaporisationheat then contributes to the removal of the reaction heat. This kind ofoperation is called condensed mode and variations of it are disclosed,among others, in WO-A-2007/025640, U.S. Pat. No. 4,543,399, EP-A-699213and WO-A-94/25495. It is also possible to add condensing agents into therecycle gas stream, as disclosed in EP-A-696293. The condensing agentsare non-polymerisable components, such as n-pentane, isopentane,n-butane or isobutane, which are at least partially condensed in thecooler.

The gas is then compressed and recycled into the inlet chamber of thereactor. Prior to the entry into the reactor fresh reactants areintroduced into the fluidisation gas stream for compensating lossescaused by the reaction and product withdrawal. It is generally known toanalyse the composition of the fluidisation gas and introduce the gascomponents to keep the composition constant. The actual gas compositionis determined by the desired properties of the product and the catalystused in the polymerisation.

The top part of the gas phase reactor may include a so calleddisengagement zone. In such a zone the diameter of the reactor isincreased to reduce the gas velocity and allow the particles that arecarried from the bed with the fluidisation gas to settle back to thebed.

The bed level may be observed by different techniques known in the art.For instance, the pressure difference between the bottom of the reactorand a specific height of the bed may be recorded over the whole lengthof the reactor and the bed level may be calculated based on the pressuredifference values. Such a calculation yields a time-averaged level. Itis also possible to use ultrasonic sensors or radioactive sensors. Withthese methods instantaneous levels may be obtained, which of course maythen be averaged over time to obtain a time-averaged bed level.

Also antistatic agent(s) may be introduced into the gas phase reactor ifneeded. Suitable antistatic agents and methods to use them aredisclosed, among others, in U.S. Pat. No. 5,026,795, U.S. Pat. No.4,803,251, U.S. Pat. No. 4,532,311, U.S. Pat. No. 4,855,370 andEP-A-560035. They are usually polar compounds and include, among others,water, ketones, aldehydes and alcohols.

The reactor may also include a mechanical agitator to further facilitatemixing within the fluidised bed. An example of suitable agitator designis given in EP-A-707513.

The polymeric product may be withdrawn from the gas phase reactor eithercontinuously or intermittently. Continuous withdrawal is preferred.Combinations of these methods may also be used. Continuous withdrawal isdisclosed, among others, in WO-A-00/29452. Intermittent withdrawal isdisclosed, among others, in U.S. Pat. No. 4,621,952, EP-A-188125,EP-A-250169 and EP-A-579426.

Third Polymerisation Reactor

In the third polymerisation reactor a heterophasic copolymer comprisingthe first polymer mixture and a third copolymer of propylene is formed.This is done by introducing the particles of the first polymer mixture,containing active catalyst dispersed therein, together with additionalpropylene and comonomer into the third polymerisation reactor. Hydrogenmay be introduced for controlling the molecular weight. This causes thethird copolymer to form on the particles containing the first polymermixture.

The melt index MFR₂ of the heterophasic copolymer is from 0.05 to 2.0g/10 min, preferably from 0.1 to 1.0 g/10 min and more preferably from0.15 to 0.5 g/10 min.

As explained above for the first polymer mixture, the MFR₂ of the thirdcopolymer of propylene cannot be measured because the third copolymercannot be isolated from the heterophasic copolymer. However, the MFR₂ ofthe third copolymer of propylene can be calculated by using equation 1above. In that case the component 1 is the first polymer mixture,component 2 is the third copolymer and the final blend is theheterophasic copolymer. It can then be found that the MFR₂ of the thirdcopolymer is about the same as the MFR₂ of the first polymer mixture. Itis also possible to estimate the MFR₂ of the third copolymer ofpropylene by analysing the intrinsic viscosity of the polymer fractionwhich remains soluble in xylene at 25° C., measured according to ISO16152.

Hydrogen feed is adjusted to achieve a desired melt flow rate (ormolecular weight) of the polymer. Suitably, the hydrogen feed iscontrolled to maintain constant hydrogen to propylene ratio in thereaction mixture. The actual ratio depends on the catalyst as well asthe type of the polymerisation. Good results have been obtained in gasphase polymerisation by maintaining the ratio within the range of from 1to 100 mol/kmol, preferably from 2 to 80 mol/kmol.

The third copolymer is elastomeric. By “elastomeric” is meant that thethird copolymer is substantially amorphous, having substantially nocrystalline fraction. Additionally or alternatively, the third copolymerremains soluble in xylene at 25° C., measured according to ISO 16152.

The comonomer is selected from ethylene, alpha-olefins containing 4 to10 carbon atoms and their mixtures. The comonomer used in the thirdpolymerisation reactor may be the same as or different from thecomonomer used in the preceding polymerisation reactors, if any had beenused. Especially preferably, ethylene is used as the comonomer in thethird polymerisation reactor.

The content of the comonomer is controlled to obtain the desiredcomonomer content of the heterophasic copolymer. Typically theheterophasic copolymer contains from 5 to 25% by mole of units derivedfrom the comonomer and from 75 to 95% by mole of propylene units.Preferably the heterophasic copolymer contains from 5.0 to 20% by moleof units derived from the comonomer and from 80 to 95.0% by mole ofpropylene units.

As discussed above for the first polymer mixture the comonomer contentof the third copolymer cannot be directly measured.

According to one method the comonomer content of the third copolymer canbe calculated by using equation 2 above. In that case the component 1 isthe first polymer mixture, component 2 is the third copolymer and thefinal blend is the heterophasic copolymer. Typically, the thirdcopolymer of propylene comprises from 35 to 75% by mole of comonomerunits and from 25 to 65% by mole of propylene units. Preferably thethird copolymer of propylene comprises from 35 to 70% by mole ofcomonomer units and from 30 to 65% by mole of propylene units.

According to another method, the comonomer content of the thirdcopolymer is determined from the polymer fraction which remains solublein xylene at 25° C. The comonomer content is measured from this fractionaccording to the methods known to the person skilled in the art.

The comonomer to propylene ratio that is needed to produce the desiredcomonomer content in the polymer depends, among others, on the type ofcomonomer and the type of catalyst. With ethylene as a comonomer goodresults have been obtained in gas phase polymerisation with a molarratio of ethylene to propylene of 200 to 700 mol/kmol, preferably from250 to 650 mol/kmol and in particular from 300 to 600 mol/kmol.

The heterophasic copolymer comprises from 65 to 86% by weight of thefirst polymer mixture, preferably from 70 to 86%, and from 14 to 35% byweight of the third copolymer, preferably from 14 to 30%. As discussedabove, preferably the first and second polymers are homopolymers and thethird polymer is a copolymer of propylene and ethylene.

The content of the xylene soluble polymer at 25° C. in the thirdcopolymer cannot be directly measured. The amount can be estimated byusing equation 4 above In that case the component 1 is the first polymermixture, component 2 is the third polymer and the final blend is theheterophasic copolymer. The third polymer typically can be found to havea content of xylene soluble polymer of at least 80% by weight,preferably at least 90% by weight, such as at least 95% by weight.

The third polymerisation stage is preferably conducted in a fluidisedbed gas phase reactor as described above for the second polymerisationstage.

Post Reactor Treatment

When the polymer mixture has been removed from the third polymerisationreactor it is subjected to process steps for removing residualhydrocarbons from the polymer. Such processes are well known in the artand can include pressure reduction steps, purging steps, strippingsteps, extraction steps and so on. Also combinations of different stepsare possible.

According to one preferred process a part of the hydrocarbons is removedfrom the polymer powder by reducing the pressure. The powder is thencontacted with steam at a temperature of from 90 to 110° C. for a periodof from 10 minutes to 3 hours. Thereafter the powder is purged withinert gas, such as nitrogen, over a period of from 1 to 60 minutes at atemperature of from 20 to 80° C.

According to another preferred process the polymer powder is subjectedto a pressure reduction as described above. Thereafter it is purged withan inert gas, such as nitrogen, over a period of from 20 minutes to 5hours at a temperature of from 50 to 90° C.

The purging steps are preferably conducted continuously in a settledmoving bed. The polymer moves downwards as a plug flow and the purgegas, which is introduced to the bottom of the bed, flows upwards.

Suitable processes for removing hydrocarbons from polymer are disclosedin WO-A-02/088194, EP-A-683176, EP-A-372239, EP-A-47077 andGB-A-1272778.

After the removal of residual hydrocarbons the polymer mixture ispreferably mixed with additives as it is well known in the art. Suchadditives include antioxidants, process stabilizers, neutralizers,lubricating agents, nucleating agents, pigments and so on.

The polymer mixture is then extruded to pellets as it is known in theart. Preferably a co-rotating twin screw extruder is used for theextrusion step. Such extruders are manufactured, for instance, byCoperion and Japan Steel Works.

Heterophasic Copolymer

The heterophasic copolymer produced according to the process of thepresent invention is a copolymer of propylene with a comonomer selectedfrom the group consisting of ethylene, alpha-olefins having from 4 to 10carbon atoms, and mixtures thereof. Preferably there is only onecomonomer and especially preferably the comonomer is ethylene. Typicallythe heterophasic copolymer comprises from 5 to 25% by mole of unitsderived from the comonomer and from 75 to 95% by mole of propyleneunits.

The heterophasic copolymer produced according to the process of thepresent invention has MFR₂ of from 0.05 to 2.0 g/10 min, preferably from0.1 to 1.0 g/10 min and more preferably from 0.15 to 0.5 g/10 min.

The heterophasic copolymer produced according to the process of thepresent invention preferably has a fraction of xylene soluble polymerdetermined according to ISO 16152 of from 14 to 35% by weight, morepreferably from 14 to 30% by weight.

It is further preferred that the intrinsic viscosity measured from theamorphous polymer fraction, i.e., the fraction which remains soluble inxylene at 25° C. and precipitates upon addition of acetone, is from 1.5to 4.4 dl/g, more preferably from 2.0 to 4.4 dl/g. Alternatively oradditionally, the content of comonomer units measured from the amorphouspolymer fraction is preferably from 35 to 75% by mole and morepreferably from 35 to 70% by mole, such as from 35 to 60% by mole.

The heterophasic copolymer produced according to the process of thepresent invention preferably has a total content of comonomer units offrom 5.0 to 20% by mole and the content of units derived from propyleneof from 80 to 95% by mole.

The heterophasic copolymer produced according to the process of thepresent invention preferably has a flexural modulus of from 700 to 1700MPa, more preferably from 750 to 1600 MPa. It preferably further has anotched Charpy impact strength measured at -20° C. measured according toIS0179 using specimen 1eA of at least 3.5 kJ/m², more preferably atleast 4.0 kJ/m². Said notched Charpy impact strength measured at -20° C.will normally not exceed a value of 30 kJ/m². Said notched Charpy impactstrength measured at 23° C. will normally have a value from 75 to 150kJ/m².

The heterophasic copolymer produced according to the process of thepresent invention does not contain any phthalic acid esters which wouldoriginate from the manufacturing process.

Due to the increased productivity the resulting polymer has a reducedcontent of catalyst residues, such as residual titanium, magnesiumand/or aluminium. For instance, the magnesium content in theheterophasic copolymer is preferably not more than 30 ppm and morepreferably not more than 20 ppm. Normally it is not possible to avoidmagnesium in the polymer altogether and the content is typically atleast 1 ppm, like at least 2 ppm. While it is possible to reduce thecontent further by washing the polymer, for instance, with alcohols thisadds complexity to the process and increases the investment andoperating costs thereof. Therefore washing steps are usually notpreferred.

Thus, the heterophasic copolymer produced according to the process ofthe present invention has a broad molecular weight distribution combinedwith a low level of catalyst residues and it does not contain anyphthalate originating from the production process.

Especially, the heterophasic copolymer comprises:

-   -   (1) A first polymer of propylene, selected from homopolymers of        propylene and random copolymers of propylene containing from 0.1        to 5% by mole of a comonomer selected from the group consisting        of ethylene, alpha-olefins having from 4 to 10 carbon atoms, and        mixtures thereof and having a melt flow rate MFR₂ of from 0.1 to        4.0 g/10 min;    -   (2) a second polymer of propylene, selected from homopolymers of        propylene and random copolymers of propylene containing from 0.1        to 5% by mole of a comonomer selected from the group consisting        of ethylene, alpha-olefins having from 4 to 10 carbon atoms, and        mixtures thereof and having a melt flow rate MFR₂ of from 0.05        to 0.3 g/10 min and which is less than the MFR₂ of the first        polymer of propylene;    -   (3) a third polymer of propylene selected from random copolymers        of propylene containing from 35 to 75% by mole of units of a        comonomer selected from the group consisting of ethylene,        alpha-olefins having from 4 to 10 carbon atoms and mixtures        thereof.

Preferably the first polymer of propylene and the second polymer ofpropylene are homopolymers of propylene. Further, preferably the thirdpolymer is a copolymer of propylene and ethylene.

Furthermore, the heterophasic copolymer preferably comprises from 24 to59% by weight of the first polymer of propylene, from 28 to 64% byweight of the second polymer of propylene and from 2 to 30% by weight ofthe third polymer of propylene. The percentage figures are based on thetotal weight of the heterophasic copolymer. Especially preferably, thefirst and second polymers of propylene are present in such amounts thatthe ratio of the weight of the first polymer to the weight of the secondpolymer is from 35:65 to 60:40 and the third polymer is present in suchamount that the ratio of the combined weight of the first and secondpolymers of propylene to the weight of the third polymer of propylene isfrom 70:30 to 98:2.

Such heterophasic copolymer has the properties as defined above, andespecially MFR₂ and content of comonomer units as defined above.

Pipes Made of Heterophasic Copolymers

Furthermore, the present invention relates to sheets, profiles,fittings, and pipes, like pipe fittings, in particular non-pressurepipes, comprising, preferably comprising at least 75 wt.-%, morepreferably comprising at least 90 wt.-%, like at least 95 wt.-%, mostpreferably consists of, a heterophasic copolymer as defined in theinstant invention.

The term “pipe” as used herein is meant to encompass hollow articleshaving a length greater than diameter. Moreover the term “pipe” shallalso encompass supplementary parts like fittings, valves and all partswhich are commonly necessary for e.g. a indoor soil and waste orunderground sewage piping system.

Pipes according to the invention encompass solid wall pipes andstructured wall pipes. Solid wall pipes can be single layer pipes ormultilayer pipes, however it is preferred that the solid wall pipe is asingle layer pipe. Structured wall pipes preferably consist of twolayers, one of which is a smooth inner layer while the other is acorrugated, spiral wound or ribbed outer layer. More preferably theinventive composition is comprised in at least one of the layers of sucha structured wall pipe.

The heterophasic copolymer used for pipes according to the invention maycontain usual auxiliary materials, e. g. up to 10 wt.-% fillers and/or0.01 to 2.5 wt.-% stabilizers and/or 0.01 to 10 wt.-% processing aidsand/or 0.1 to 1.0 wt.-% antistatic agents and/or 0.2 to 3.0 wt.-%pigments and/or reinforcing agents, e. g. glass fibres, in each casebased on the heterophasic copolymer used (the wt.-% given in thisparagraph refer to the total amount of the pipe and/or a pipe layercomprising said heterophasic copolymer).

Benefits of the Invention

The heterophasic copolymers of the invention are produced in a mannerwhere polymer with higher melt flow rate is produced in the firstpolymerisation reactor and polymer with lower melt flow rate is producedin the second polymerisation reactor. In this way a greater productivityof the catalyst can be obtained. This gives very good impact strength tothe heterophasic copolymers both at ambient and sub-zero temperaturesresulting from combination of high amount of xylene soluble fractionwith low intrinsic viscosity of amorphous polymer. Typically multiplereactors are operated in a manner where lower melt flow rate polymers isproduced in the first reactor and higher melt flow rate polymer isproduced in the second reactor. The productivity of the catalyst islower in this manner and the polymers produced have lower impactstrength values.

Description of Methods

Melt Flow Rate

Melt flow rate (MFR, MFR₂) was determined according to ISO 1133 at 230°C. under the load of 2.16 kg.

The melt flow rate MFR₂ is herein assumed to follow the following mixingrule (equation 1):

$\begin{matrix}{{MI}_{b} = ( {{w_{1} \cdot {MI}_{1}^{- 0.0965}} + {w_{2} \cdot {MI}_{2}^{- 0.0965}}} )^{- \frac{1}{0.0965}}} & ( {{eq}.\mspace{14mu} 1} )\end{matrix}$

Where w is the weight fraction of the component in the mixture, MI isthe melt index MFR₂ and subscripts b, 1 and 2 refer to the mixture,component 1 and component 2, respectively.

Content of Comonomer

Ethylene content, i.e., the content of ethylene units in propylenepolymer was measured by Fourier transmission infrared spectroscopy(FTIR). A thin film of the sample (thickness approximately 250 μm) wasprepared by hot-pressing. The area of —CH2-absorption peak (800-650cm⁻¹) was measured with Perkin Elmer FTIR 1600—spectrometer. The methodwas calibrated by ethylene content data measured by ¹³C NMR.

The comonomer content is herein assumed to follow the mixing rule(equation 2):

C _(b) =w ₁ ·C ₁ +w ₂ ·C ₂   (eq. 2)

where C is the content of comonomer in weight-%, w is the weightfraction of the component in the mixture and subscripts b, 1 and 2 referto the overall mixture, component 1 and component 2, respectively.

Xylene Soluble

The amount of xylene soluble fraction was determined according to ISO16152, 5^(th) edition (2005-07-01). The amount of polymer which remainsdissolved at 25° C. is given as the amount of xylene soluble polymer.

The amorphous polymer (AM) is obtained by separating the xylene solublepolymer from the undissolved polymer and precipitating the amorphouspolymer from the solution with acetone (100 ml acetone per 100 ml ofsolution) at 25° C.

The content of xylene soluble polymer is herein assumed to follow themixing rule (equation 4):

XS _(b) =w ₁ ·XS ₁ +w ₂ ·XS ₂   (eq.4)

Where XS is the content of xylene soluble polymer in weight-%, w is theweight fraction of the component in the mixture and subscripts b, 1 and2 refer to the overall mixture, component 1 and component 2,respectively.

Flexural Modulus

The flexural modulus was determined in 3-point-bending at 23° C.according to ISO 178 on 80×10×4 mm³ test bars injection moulded in linewith EN ISO 1873-2.

Charpy Notched Impact Strength

Charpy notched impact was measured according to ISO 179/1eA at +23° C.and at −20° C. on 80×10×4 mm³ test bars injection moulded in line withEN ISO 1873-2.

Intrinsic Viscosity

The intrinsic viscosity (iV) value increases with the molecular weightof a polymer. The iV values e.g. of the XCS were measured according toISO 1628/1 in decalin at 135° C. The iV(AM) was measured from theamorphous polymer in similar manner.

Comonomer Content

Quantitative Fourier transform infrared (FTIR) spectroscopy was used toquantify the amount of comonomer. The content of comonomer units wasmeasured from a 300 μm thick film pressed from the polymer. The film waspressed at 180° C. in a conventional manner using a mould with 28 mmdiameter. The film was inspected to confirm the absence of air bubbles.Calibration was achieved by correlation to comonomer contents determinedby quantitative nuclear magnetic resonance (NMR) spectroscopy.

The calibration procedure based on results obtained from quantitative¹³C-NMR spectroscopy was undertaken in the conventional manner welldocumented in the literature.

The amount of comonomer (N) was determined as weight percent (wt %) via:

N=k1(A/R)+k2

wherein A is the maximum absorbance defined of the comonomer band, R themaximum absorbance defined as peak height of the reference peak and withk1 and k2 the linear constants obtained by calibration. The band usedfor ethylene content quantification is selected depending if theethylene content is random (730 cm⁻¹) or block-like (720 cm-¹). Theabsorbance at 4324 cm⁻¹ was used as a reference band.

The C₂(AM) was measured from the amorphous polymer in similar mannerexcept that the thickness of the film was 100 μm.

Ash Content

The total ash content of the polymer was measured by combusting thepolymer in an oven at 750° C. The polymer sample (about 20 grams) wasweighed into a platinum fire pot. Then the pot containing the sample wasplaced into the oven and kept there at 750° C. for 15 minutes. The potwas weighed and the amount of ash in the pot was determined. The ashcontent was given as the fraction of the residual material from thetotal polymer amount.

Magnesium Content

The content of magnesium was determined from the ash. The ash obtainedfrom the combustion as described above was dissolved in 5 ml nitric acidunder heating so that the ash sample dissolved. The solution was thendiluted with distilled water to 100 ml and filtered through a 0.45 μmfilter. The metal content was determined from the filtered solution byICP (Inductively Coupled Plasma).

EXAMPLES

Catalyst Preparation

Used Chemicals:

2-ethylhexanol, provided by Amphochem

3-Butoxy-2-propanol—(DOWANOL™ PnB), provided by Dow

bis(2-ethylhexyl)citraconate, provided by SynphaBase

TiCl₄, provided by Millenium Chemicals

Toluene, provided by Aspokem

Viscoplex® 1-254, provided by Evonik

Heptane, provided by Chevron

3.4 litre of 2-ethylhexanol and 810 ml of propylene glycol butylmonoether (in a molar ratio 4/1) were added to a 20 l reactor. Then 7.8litre of a 20% solution in toluene of BEM (butyl ethyl magnesium)provided by Crompton GmbH, were slowly added to the well stirred alcoholmixture. During the addition the temperature was kept at 10° C. Afteraddition the temperature of the reaction mixture was raised to 60° C.and mixing was continued at this temperature for 30 minutes. Finallyafter cooling to room temperature the obtained Mg-alkoxide wastransferred to a storage vessel.

21.2 g of Mg alkoxide prepared above was mixed with 4.0 mlbis(2-ethylhexyl) citraconate for 5 min. After mixing the obtained Mgcomplex was used immediately in the preparation of the catalystcomponent.

19.5 ml of titanium tetrachloride was placed in a 300 ml reactorequipped with a mechanical stirrer at 25° C. Mixing speed was adjustedto 170 rpm. 26.0 g of Mg-complex prepared above was added within 30minutes keeping the temperature at 25° C. 3.0 ml of Viscoplex® 1-254 and1.0 ml of a toluene solution with 2 mg Necadd 447™ was added. Then 24.0ml of heptane was added to form an emulsion. Mixing was continued for 30minutes at 25° C., after which the reactor temperature was raised to 90°C. within 30 minutes. The reaction mixture was stirred for a further 30minutes at 90° C. Afterwards stirring was stopped and the reactionmixture was allowed to settle for 15 minutes at 90° C. The solidmaterial was washed 5 times: Washings were made at 80° C. under stirringfor 30 min with 170 rpm. After stirring was stopped the reaction mixturewas allowed to settle for 20-30 minutes and followed by siphoning.

Wash 1: Washing was made with a mixture of 100 ml of toluene and 1 mldonor

Wash 2: Washing was made with a mixture of 30 ml of TiCl₄ and 1 ml ofdonor.

Wash 3: Washing was made with 100 ml of toluene.

Wash 4: Washing was made with 60 ml of heptane.

Wash 5: Washing was made with 60 ml of heptane under 10 minutesstirring.

Afterwards stirring was stopped and the reaction mixture was allowed tosettle for 10 minutes while decreasing the temperature to 70° C. withsubsequent siphoning, followed by N₂ sparging for 20 minutes to yield anair sensitive powder.

Example 1

A stirred tank reactor having a volume of 45 dm³ was operated asliquid-filled at a temperature of 30° C. and a pressure of 54 bar. Intothe reactor was fed propylene so much that the average residence time inthe reactor was 0.36 hours together with 0.98 g/h hydrogen, 70 g/h ofethylene and 4.3 g/h of a polymerisation catalyst prepared according toCatalyst Preparation Example above with triethyl aluminium (TEA) as acocatalyst and dicyclopentyldimethoxysilane (DCPDMS) as external donorso that the molar ratio of TEA/Ti was about 76 mol/mol and TEA/DCPDMSwas 8 mol/mol. The slurry from this prepolymerisation reactor wasdirected to a loop reactor having a volume of 150 dm³ together with 170kg/h of propylene and hydrogen so that the molar ratio of hydrogen topropylene was 0.12 mol/kmol. The loop reactor was operated at atemperature of 80° C. and a pressure of 51 bar. The production rate ofpropylene copolymer was 29 kg/h and the melt flow rate MFR₂ was 0.56g/10 min.

The polymer slurry from the loop reactor was directly conducted into afirst gas phase reactor operated at a temperature of 80° C. and apressure of 25 bar. Into the reactor were fed additional propylene andhydrogen, as well as nitrogen as inert gas, so that the content ofpropylene was 83% by mole and the ratio of hydrogen to propylene was 1mol/kmol. The production rate in the reactor was 47 kg/h and the polymerwithdrawn from the reactor had a melt flow rate MFR₂ of 0.34 g/10 min.The split of the polymer produced in the loop reactor to the polymerproduced in the gas phase reactor was 38:62.

The polymer from the first gas phase reactor was conducted into a secondgas phase reactor operated at a temperature of 70° C. and a pressure of16 bar. Into the reactor were fed additional propylene, ethylene andhydrogen, as well as nitrogen as inert gas, so that the content ofpropylene was 63% by mole, the ratio of ethylene to propylene was 310mol/kmol, the ratio of hydrogen to ethylene was 22 mol/kmol and theratio of hydrogen to propylene was 7 mol/kmol. The production rate inthe reactor was 11 kg/h. The polymer was withdrawn from the reactor andthe hydrocarbons were removed by purging with nitrogen. The resultingpolymer had a melt flow rate MFR₂ of 0.25 g/10 min and an ethylenecontent of 7.3% by weight. The split of the polymer produced in the loopand the first gas phase reactors to the polymer produced in the secondgas phase reactor was 86:14.

The polymer powder withdrawn from the reactor was mixed with acombination of 0.1 wt % of Pentaerythrityl-tetrakis(3-(3′,5′-di-tert.butyl-4-hydroxyphenyl)-propionate (CAS No. 6683-19-8, commerciallyavailable as Irganox 1010 from BASF AG, Germany) and 0.1 wt % of Tris(2,4-di-t-butylphenyl) phosphite (CAS No. 31570-04-4, commerciallyavailable as Irgafos 168 from BASF AG, Germany) as antioxidants, and0.05 wt % of calcium stearate (CAS No. 1592-23, commercially availableas Calcium stearate SP from Faci SpA, Italy) as acid scavenger. Themixture of polymer and additives was then extruded to pellets by using aZSK70 extruder (product of Coperion, Germany) under nitrogen atmosphereat a barrel temperature of 200-240° C., followed by strand pelletisationafter cooling in a water bath. The resulting polymer pellets weresubsequently used for characterization.

Example 2

The procedure of Example 1 was followed except that the operationconditions in the loop reactor and the gas phase reactors were modifiedas shown in Table 1.

Examples 3 and 4

The procedure of Example 1 was repeated except that the TEA/Ti ratio wasabout 68 mol/mol, the TEA/DCPDMS ratio was 8 mol/mol and the catalystfeed rate was 6.1 g/h. Further, the conditions were as indicated inTable 1.

Comparative Example 1

The procedure of Example 1 was followed except that the operationconditions in the loop reactor and the gas phase reactors were modifiedas shown in Table 1.

Comparative Example 2

The solid catalyst component was prepared according to Inventive Example1 of EP 2796501 A1. The process was conducted as in Inventive Example 1of EP 2796501 Al.

Comparative Example 3

The solid catalyst component was prepared according to Example 2 in WO00/68315. The process was conducted as in Inventive Example 1 in EP2539398 A1.

From Table 2 it can be seen that the resulting polymers arecharacterized by a low melt flow rate (MFR), making them especiallysuitable for extrusion processes and especially for pipe extrusion forproducing pipes having good low-temperature toughness. The very hightoughness of these heterophasic copolymers both at ambient and sub-zerotemperatures result from combination of high amount of xylene solublefraction with a limited intrinsic viscosity of the amorphous copolymer.

TABLE 1 Polymerisation conditions and some properties measured from thepolymer Example 1 2 3 4 CE1 CE2 CE3 Prepol Temperature, ° C. 30 30 20 2020 33 30 Loop Temperature, ° C. 80 80 80 80 80 72 68 Loop H₂/C₃ mol/kmol0.12 0.16 0.23 0.22 0.044 0.53 0.04 Loop C₂/C₃ mol/kmol 0 0 0 0 0 0 6Loop MFR₂, g/10 min 0.56 0.42 0.67 0.62 0.12 0.87 0.044 Loop XS, % byweight 4.0 ND 2.5 2.5 3.2 5.1 8 GPR1 Temperature, ° C. 80 80 80 80 80 8080 GPR1 Pressure, Bar 25 25 20 20 20 29 19 GPR1 H₂/C₃ mol/kmol 1 1 0.30.2 0.8 1.9 31 GPR1 MFR₂, g/10 min 0.34 0.34 0.34 0.31 ND 0.36 0.66 GPR1C₂/C₃ mol/kmol 0 0 0 0 0 0 22 GPR1 XS, % by weight 1.6 1.5 2.0 2.0 2.14.5 4.5 Split, Loop:gpr1 38:62 41:59 58:42 58:42 52:48 41:59 27:73 GPR2Temperature, ° C. 70 65 65 61 60 80 90 GPR2 Pressure, Bar 16 16 16 16 1624 27 GPR2 H₂/C₃ mol/kmol 7 6 75 73 75 0.47 0 GPR2 C₂/C₃ mol/kmol 310330 570 550 550 50 0 Final MFR₂, g/10 min 0.25 0.24 0.43 0.33 0.30 0.270.34 Final C₂-content % by weight 7.3 (11)  6.8 (9.9) 12 (17) 12 (16) 9.7 (13.9) 4.0 (5.9) 2.6 (mole) Final XS, % by weight 15 18 23 25 27 ND4.1 Split (Loop + gpr1):gpr2 86:14 83:17 78:22 75:25 74:26 94:6  92:8 IV of AM, dl/g 4.3 4.1 2.5 2.3 2.3 ND ND C₂-content % of AM % by weight37 (47) 37 (47) 42 (52) 44 (54) 42 (52) ND ND (mole) Total catalystproductivity, kg 18 17 13 14 4.0 ND ND PP/g cat Mg-content in polymer,ppm 9 9 12 11 40 ND ND ND = not determined; AM denotes the fractionwhich remains soluble in xylene at 25° C.

TABLE 2 Polymer characteristics Example 2 3 4 CE2 CE3 MFR 230° g/10 min0.24 0.43 0.33 0.27 0.34 C./2.16 kg Flex. MPa 1320 808 869 1000 1160modulus ISO178 Charpy 104 88 83 60 13.8 NIS kJ/m² ISO179 1eA 23° C.Charpy NIS kJ/m² ND ND ND 8.2 4.4 ISO179 1eA 0° C. Charpy NIS kJ/m² 8.36.6 4.4 ND ND ISO179 1eA −20° C.

1-16. (canceled)
 17. A process for producing a heterophasic copolymercomposition comprising propylene monomer and a comonomer selected fromethylene, alpha-olefins having 4 to 10 carbon atoms and their mixtures,in the presence of an olefin polymerisation catalyst comprising a solidcatalyst component further comprising titanium, magnesium, halogen andan internal donor, and a cocatalyst, the process comprising the stepsof: (1) introducing streams of the solid catalyst component, thecocatalyst, propylene monomer and hydrogen into a first polymerisationreactor; (2) producing a first polymer of propylene in the firstpolymerisation reactor, the first polymer of propylene having a firstmelt flow rate MFR2 of from 0.1 to 2.0 g/10 min; (3) withdrawing astream comprising the first polymer of propylene from the firstpolymerisation reactor and passing it to a second polymerisationreactor; (4) introducing a stream of propylene monomer into the secondpolymerisation reactor; (5) producing a first polymer mixture comprisingthe first polymer of propylene and a second polymer of propylene in thesecond polymerisation reactor, the first polymer mixture having a secondmelt flow rate MFR2 of from 0.05 to 1.0 g/10 min and which second meltflow rate is less than the first melt flow rate; (6) withdrawing astream comprising the first polymer mixture from the secondpolymerisation reactor and passing it to a third polymerisation reactor;(7) introducing streams of propylene monomer and the comonomer into thethird polymerisation reactor; (8) producing the heterophasic copolymercomposition comprising the first polymer mixture and a third copolymerof propylene in the third polymerisation reactor, the heterophasiccopolymer composition having a third melt flow rate MFR2 of from 0.05 to1.0 g/10 min, said heterophasic copolymer having a content of comonomerunits of from 5 to 25% by mole; wherein the amount of xylene solublefraction in the heterophasic copolymer determined according to ISO 16152is from 14 to 35% by weight and intrinsic viscosity measured from theamorphous polymer (AM) of the heterophasic copolymer is from 1.5 to 4.4dl/g; and (9) recovering the heterophasic copolymer composition from thethird polymerisation reactor; characterised in that the internal donoris a compound having the structure according to formula (I):

wherein R₁ and R₂ are the same or different being a linear or branchedC₁-C₁₂-alkyl group and R is hydrogen or a linear, branched or cyclicC₁to C₁₂-alkyl.
 18. The process according to claim 17 wherein thecompound having the structure according to formula (I) is abis(2-ethylhexyl)citraconate.
 19. The process according to claim 17wherein the first polymer of propylene is a homopolymer of propylene.20. The process according to claim 17 wherein the second polymer ofpropylene is a homopolymer of propylene.
 21. The process according toclaim 17 wherein the first polymer mixture comprises from 35 to 60% byweight of the first polymer of propylene and from 40 to 65% by weight ofthe second polymer of propylene.
 22. The process according to claim 17wherein the heterophasic copolymer composition comprises from 65 to 86%by weight of the first polymer mixture and from 14 to 35% by weight ofthe third copolymer.
 23. The process according to claim 22 wherein theheterophasic copolymer composition comprises from 70 to 86% by weight ofthe first polymer mixture and from 14 to 30% by weight of the thirdcopolymer.
 24. The process according to claim 17 wherein the firstpolymerisation reactor is a loop reactor.
 25. The process according toclaim 17 wherein the second polymerisation reactor is a gas phasereactor.
 26. The process according to claim 17 wherein the thirdpolymerisation reactor is a gas phase reactor.
 27. The process accordingto claim 17 wherein the third polymer is a copolymer of propylene andethylene.
 28. The process according to claim 27 wherein the molar ratioof ethylene to propylene in the third polymerisation reactor is from 200to 700 mol/kmol.
 29. A heterophasic copolymer obtainable by the processof claim 17 comprising (A) a first polymer of propylene, selected fromhomopolymers of propylene and random copolymers of propylene containingfrom 0.1 to 5% by mole of a comonomer selected from the group consistingof ethylene, alpha-olefins having from 4 to 10 carbon atoms, andmixtures thereof and having a melt flow rate MFR2 of from 0.1 to 4.0g/10 min; (B) a second polymer of propylene, selected from homopolymersof propylene and random copolymers of propylene containing from 0.1 to5% by mole of a comonomer selected from the group consisting ofethylene, alpha-olefins having from 4 to 10 carbon atoms, and mixturesthereof and having a melt flow rate MFR2 of from 0.05 to 0.3 g/10 minand which is less than the MFR2 of the first polymer of propylene; (C) athird polymer of propylene selected from random copolymers of propylenecontaining from 35 to 75% by mole of units of a comonomer selected fromthe group consisting of ethylene, alpha-olefins having from 4 to 10carbon atoms and mixtures thereof; and wherein the heterophasiccopolymer contains from 1 to 30 ppm magnesium originating from thecatalyst and no phthalic acid esters originating from the catalyst. 30.The heterophasic polymer according to claim 29 wherein the heterophasiccopolymer contains from 2 to 20 ppm magnesium originating from thecatalyst.
 31. A heterophasic copolymer of propylene with a comonomerselected from the group consisting of ethylene, alpha-olefins havingfrom 4 to 10 carbon atoms, and mixtures thereof, obtainable by theprocess of claim 17, said heterophasic copolymer comprising from 5 to25% by mole of units derived from the comonomer and from 75 to 95% bymole of propylene units and being further characterized by a melt indexMFR2 of from 0.05 to 2.0 g/10 min.
 32. A pipe made of heterophasiccopolymer of propylene according to claim
 29. 33. A pipe made ofheterophasic copolymer of propylene according to claim 31.